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Chemistry > Electroloysis > Flashcards

Electroloysis Flashcards

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1
Q

what is electrolysis

A

the decomposition of an electrolyte by an electric current but the compound must be molten or in aqeuous solution

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2
Q

why do ionic compounds only conduct electricity when molten or in aqueous solution

A

the ions are free to move and carry the charge

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3
Q

why do ionic compounds not conduct electricity when solid

A

the ions are held in fixed positions in the lattice so cannot move

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4
Q

what are the electrodes made of

A

graphite/carbon/platinum as these elements are unreactive and do not react with the products of electrolysis

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5
Q

what is the anode

A

the positive electrode

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6
Q

what is the cathode

A

the negative electrode

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7
Q

what happens at the cathode

A

the positive ions are attracted to the cathode and gain electrons and are reduced

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8
Q

what happens at the anode

A

the negative ions are attracted to the anode and lose electrons and are oxidised

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9
Q

what colour is copper

A

brown solid

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10
Q

what colour is hydrogen

A

it is a colourless gas

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11
Q

what colour is oxygen

A

a colourless gas

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12
Q

what colour is chlorine

A

a pale green gas

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13
Q

what colour is bromine

A

a red-brown gas

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14
Q

what colour is copper(II) sulphate solution

A

blue

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15
Q

how is aluminium extracted

A

by the electrolysis of a molten mixture of aluminium oxide and cryolite

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16
Q

why is aluminium melted and dissolved in molten cryolite

A

the mixture has a lower melting point than aluminium oxide as cryolite lowers the temperature required to melt aluminium oxide so reduces the cost of melting aluminium oxide

17
Q

why do the anodes disappear and have to be replaced frequently

A

the anodes are made of carbon, so the oxygen reacts with carbon due to the high temperature in the cell to form carbon dioxide which escapes as a gas

18
Q

what are the reasons for recycling aluminium

A

it saves energy
natural reserves of bauxite will last longer
there is less mining of the ore

19
Q

what is produced at the cathode when an aqueous solution is electrolysed

A

the ions of the less reactive metal otherwise H plus ions

20
Q

what is produced at the anode when an aqueous solution is electrolysed

A

halide ions are preferred and discharged in preference to OH- ions but if there are no halides, then OH- ions are preferred

21
Q

why does hydrogen form at the cathode instead of sodium when an aqueous solution is electrolysed

A

hydrogen is less reactive than sodium
Hydrogen ions gain electrons more easily than sodium ions

22
Q

how do you collect and measure the volume of gas produced at the anode

A

take a graduated test tube, fill it with copper(II) chloride solution and invert it over the electrode

23
Q

what happens in the electrolysis of sodium chloride solution

A

hydrogen gas is formed at the negative electrode
chlorine gas is formed at the positive electrode
a solution of sodium hydroxide is formed as the by-product (not the main produce)

24
Q

what are the uses of hydrogen

A

in the manufacture of ammonia
in the manufacture of hydrochloric acid

25
Q

what are the uses of chlorine

A

in the manufacture of the polymer PVC
as a bleaching agent
water supply treatment

26
Q

what are the uses of sodium hydroxide

A

in the manufacture of soap, paper and ceramics
in the manufacture of rayon

27
Q

what happens in electroplating

A

the surface of one metal is coated with a thin layer of another metal

28
Q

what are the reasons for electroplating

A

to prevent an object from rusting/ to improve corrosion resistance

to improve the appearance of the object

29
Q

what is the anode in electroplating

A

the plating metal

30
Q

what is the cathode in electroplating

A

the metal object waiting to be electroplated

31
Q

what is the electrolyte in electroplating

A

a solution containing ions of the plating metal

32
Q

why is it not necessary to add more of the ionic solution during the plating process

A

because the metal ions are replaced from the metal anode

Chemistry (21 decks)

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